In U.S. Pat. No. 4,044,847 a weighing scale is shown having an optical system for sensing tare deflection by generating a moire fringe pattern indicative of the amount of load weight. The movement of the fringe pattern is sensed by a moire optical electrical transducer unit to which are attached four photodetectors. Each the photodetectors are placed effectively 90.degree. apart from each adjacent photodector as measured with respect to the cyclic moire interference pattern which moves across the photodector array. (Therefore, it can be said that the first photodetector "sees" the center of a moire fringe line while the next two detectors see opposite side edges of other such lines and the fourth detector sees the light space between such lines.) With this arrangement when the relative angle phases are 0.degree., 90.degree., 180.degree. and 270.degree., between detectors, an optimum condition known as quadrature is created. Aligning all four photodetectors substantially 90.degree. of angle phase apart, as required by the above-mentioned invention, is an extremely costly and time-consuming operation.
The present invention eliminates the aforementioned drawback of the prior system and like systems by providing a method for correcting inaccuracies inherent in broad-based tolerance manufacturing.